This is a PhaseI/II trial of TNFR:Fc in patients with polyarticular juvenile rheumatoid arthritis who have failed or are intolerant of conventional second line drug therapy. This is a two part study. In the safety, population and phamacokinetics part, the first 3 months, all patients will receive 0.4 mg/kg/dose of TNFR:Fc twice weekly subcutaneously in an open fashion. At the end of this 3 months, "responders" will enter the second part of the study-the efficacy portion. Responders will be randomized...